Incorporate latest version of Dullahan that is built using CEF 139 and target the Universal Mac build branch

[callumlinden]

Description

Description

This commit is focused on updating CEF to the latest version (v139 as of August 2025). This is captured in Issue #4498.

Originally this work was targeted against the Develop branch but because this work depends on the Apple Silicon work that is being tested in a separate branch, this PR is now targeted against that branch.

Note: It's not strictly true that the CEF update depends on the Apple Silicon work. The macOS Viewer with the updated CEF does work but because Chromium/CEF does not play well with Rosetta 2, it performs very (very) slowly. With the Intel/ARM builds of Dullahan that is part of the CEF update and the support for native Apple Silicon builds, things perform as well (in fact, much better) than before.

Some background about this work:

Because of significant changes to CEF in the 21 months since was last updated (v118, November 2023) there are additional changes required:

• Prior to CEF 120, each media instance could share a set of cache directories and it worked - mostly. After version 120, this is actively prohibited. Consequently, to update CEF to v139, cache directories are now created with a unique path name.
• Because each instance gets a brand new cache directory and the contents of each is large, the whole cef_cache folder structure is purged at startup (before the parent being created at the first media instance creation)

Known Issues

• Nothing right now. There are a lot of moving parts are a huge number of changes so it may take some time for things to settle down.

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Checklist

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• The PR is linked to a relevant issue with sufficient context.
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• All new and existing tests pass.
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• Documentation has been updated if needed.
• Any dependent changes have been merged and published in downstream modules

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Additional Notes